1. Field of Invention
This invention pertains to plating, and more particularly to plating metal oxides by a method that is indifferent to the electrical properties of the substrate.
2. Description of the Related Art
Plating technology is widely used in modern society. Typical examples include gold-plated jewelry, silver-plated dinnerware, chrome-plated automobile parts, copper-plated pots, and zinc-plated steel. Plating is also used for a variety of purposes such as corrosion resistance, surface hardening, and appearance. In addition to plating, many other techniques for coating surfaces are also known, including sputtering and anodizing.
While many methods are known for plating with electrically conductive metals such as gold and silver, very few methods are known for plating with nonconducting materials such as metal oxides. When it is desired to deposit a metal coating on a surface, it is usual that the surface to be coated, the "substrate," be electrically conducting. When an oxide coating is desired, the customary method is anodizing, a process that generates a protective coating of oxide on the surface of conducting metal. The metal oxide coating is derived from the substrate itself; it is not ordinarily derived from an element not found in the substrate.
Advantage would be served by a method of plating with metal oxides that is indifferent to the electrical properties of the substrate. Such a method of plating, for example, would be beneficial for purposes of corrosion protection or to establish superconductive oxide films on the surfaces of otherwise electrically resistive materials.
For purposes of plating with metal oxides, aqueous solutions have many advantages; virtually every element can be rendered soluble in water. This allows the possibility of plating with oxides of elements that form insoluble oxides. Moreover, aqueous solutions can be prepared in an enormous range of compositions. Solutions may contain traces of elements that can be coprecipitated or adsorbed in the metal oxide so that the electromagnetic or superconducting properties of the coating are altered in some desired way.
At the present time, techniques available for plating with metal oxides are limited. As mentioned above, one common method is anodization. However, as indicated, the method of anodization is not indifferent to the electrical properties of the substrate. Recently, Japanese researchers in their effort to coat a chrome-nickel coil with yttrium-barium-copper oxide (high temperature superconducting material) have achieved some success in using chemical vapor deposition techniques. See Nature 322, 295; (1988).
Other technologies exist which relate to oxidation of metals for a variety of different purposes but which do not include plating metal oxides on substrates. For example, in U.S. Pat. No. 4,572,797, G. L. Silver, a method was described for removing pollutants from aqueous solutions using an oxidizing agent to oxidize contaminants in order to form oxidized products which are insoluble in the liquid and precipitate therefrom. Other art which pertains to metal oxides includes U.S. Pat. No. 2,726,144, Wallis et al., pertaining to a method of precipitating cobalt hydroxide, and U.S. Pat. No. 3,875,296, B. D. Brubaker, in which the inventor proposes to grow fibers of nickel oxide or a mixture of nickel oxide and magnesium oxide in order to prepare fibrous material resistant to high temperatures. These technologies, however, do not share the intention described in the present disclosure of plating metal oxides in such a way as to preserve or achieve desirable electrical properties in either the substrate or the plate.
In light of developments in the last decade pertaining to the use and development of high-temperature superconductors, there exists a significant need for a simple and adaptable method to plate metal oxides on a variety of insulating and noninsulating substrates.